Many functions of modern devices in automotive, consumer and industrial applications, such as converting electrical energy and driving an electric motor or an electric machine, rely on semiconductor devices. Insulated Gate Bipolar Transistors (IGBTs) have been used for various applications including but not limited to switches in power supplies and power converters.
The direction of current flow through IGBTs operating as switches or motor drivers may be different in different operating cycles. When the IGBT is forward biased, i.e. when the pn-body diode at the body-drain junction of the IGBT is reversely biased, the IGBT is effective as an electronic switch capable of switching on and off a current flowing in a forward direction between a collector and an emitter terminal (metallization) by applying a gate potential to an insulated gate electrode to capacitively controlling a transistor channel in the p-type body region. The IGBT is in a “transistor mode” as long as a unipolar electron current through the transistor channel is below a threshold beyond which a voltage drop across the pn junction formed between a p-type collector region (also referred to as p-type backside emitter region and backside hole-emitter region) and an n-type drift region (also referred to as base region) arranged between the collector region and the body region is sufficiently high such that the collector region starts injecting holes into the drift region and a bipolar current flows in an “IGBT mode”. To allow low ohmic current flow through the IGBT in a “reverse mode” (also referred to as “reverse-conducting mode” or “diode mode”), in which the pn-body diode is forwardly biased, a structured collector region having portions of both doping types may be provided. The loss of the thereby monolithically integrated free-wheeling diode is, in reverse mode of the IGBT, mainly determined by the product of current flow and voltage drop across the body diode and the drift region. IGBTs with monolithically integrated free-wheeling diodes are also termed “reverse-conducting IGBTs” (rc-IGBTs). These semiconductor devices avoid inductances and capacitances associated with the required contacts and supply lines of external free-wheeling diodes.
Typically, improving the characteristics of one mode of multi-mode rc-IGBTs adversely affects another mode. It is desirable to improve the device characteristics of RC-IGBTs with less adverse impact on other device characteristics.